1. Field of the Invention
The present invention relates to an ophthalmologic apparatus.
2. Description of the Related Art
An optical coherence tomography (OCT) imaging apparatus such as an OCT allows three-dimensional observation of a state within retinal layers. Such an optical coherence tomography imaging apparatus is recently attracting attention as being useful in more accurately diagnosing diseases.
A time domain OCT (TD-OCT) is a type of OCT in which a broad spectrum light source is combined with a Michelson interferometer. The TD-OCT scans a delay in a reference arm to measure the interference light generated by a backscattered light of a signal arm and the light from the reference arm interfering with each other, and acquires information on depth resolution. However, high-speed image acquisition is difficult when such TD-OCT is used. In contrast, a spectral domain OCT (SD-OCT) in which a spectroscope acquires an interferogram by employing the broad spectrum light source is capable of capturing the image at higher speed. Further, U.S. Pat. No. 5,321,501 discusses a swept source OCT (SS-OCT) in which a single channel light detection device measures spectral interference by employing a high-speed swept light source as the light source.
Since the spectroscope in the SD-OCT disperses the interference light using a diffraction grating, crosstalk by the interference light tends to occur between adjacent pixels of a line sensor. Further, the interference light from a reflection surface positioned at a depth position Z=Z0 vibrates at a frequency of Z0/πwith respect to a wave number k. A vibration frequency of the interference light thus increases as Z0 increases (i.e., the reflection surface moves away from a coherence gate position), so that the effect of the crosstalk by the interference light between the adjacent pixels in the line sensor increases. As a result, when the SD-OCT performs imaging at a deeper position, sensitivity is lowered. In contrast, the SS-OCT which does not use the spectroscope is advantageous as compared to the SD-OCT in being capable of capturing the tomographic image at a deeper position.
Furthermore, in the SD-OCT, there is a loss of interference light caused by the diffraction grating in the spectroscope. On the other hand, the SS-OCT which does not include the spectroscope is capable of easily improving the sensitivity by performing differential detection of the interference light. The SS-OCT is thus capable of performing high-speed processing at the same level of sensitivity as the SD-OCT, and of capturing a tomographic image of a wide viewing angle employing the high-speed capability.
Moreover, Japanese Patent Application Laid-Open No. 2007-117714 discusses the SD-OCT which displays the tomographic image and the fundus image side by side in a horizontal direction of a display area on the display unit.
However, if the tomographic image of a wide viewing angle acquired by the SS-OCT is displayed side by side with the fundus image, it becomes necessary to display a reduced tomographic image, or display a portion of the tomographic image due to the limit on the size of the display area. The tomographic image captured by the SS-OCT thus cannot be efficiently displayed.